Constantly looking for newer and better utilities to use on behalf of our clients, we recently came across a program called MalwareBytes' Anti-Malware. Upon investigation, we found that it had the respect of many of my long-time colleagues and, as such, decided to give it a try in some testbeds. We found it to be superior to anything else we had used for spyware detection and removal up to that time: namely, Lavasoft's Ad-Aware, Safer Networking's Spybot Search & Destroy, and BillP Studios' WinPatrol.
In the tests that we ran, it found approximately three to five times as many infections as the other utilities combined and did so in about half the time that it took to run the other three utilties. This ends up cleaning the client's machine more thoroughly as well as allowing the client to receive his machine back that much sooner.
This is one of the best programs that you can get to clean your machine. While it does not run in the background, it doesn't need to do so if you have Norton Security. Run the program on a weekly basis (making sure to get all program and definition updates first) and you will keep your machine free of infection-related problems.